U. LEEDS (UK)—Attempting to get a quick tan during summer vacation—especially after being covered up for most of the rest of the year—is a sure way to raise the risk of melanoma, a serious form of skin cancer that can spread rapidly.

Researchers at the University of Leeds studied the genetic make-up of around 1,500 men and women with varying numbers of moles. Participants were also asked how often they exposed their skin to the sun.

Results showed that a combination of genes and behavior appear to determine if and how many moles, or nevi, will develop.

People with certain genes on chromosomes 9 and 22 were more likely to have a lot of moles and that these moles tended to be bigger.

A gene on chromosome 6 was linked to large moles but this gene did not increase the number of nevi.

At the same time, people with a history of getting sunburn and who exposed their skin to the sun on holidays rather than moderately throughout the year were more likely to have a lot of moles. Holiday sun exposure was also linked to large moles.

Men and women who spend a lot of time outdoors and often exposed their arms and legs to the elements regularly, but without burning, were less likely to have a lot of moles.

Taken together, these findings suggest that people who already have lots of moles—because of their genetic makeup—should be particularly careful not to get burned and would be well advised to adopt a little and often approach.

“Like many illnesses, the reason we get skin cancer is partly due to our genes and partly due to our lifestyle or environment,” says Julia Newton-Bishop, professor of dermatology.

“What we want is for individuals to understand their own level of risk so they can modify their behavior accordingly. This is all about knowing your own skin.

“It is no coincidence that women tend to have most moles on their lower legs. That’s because at the first sign of sun, the first thing many women do is try and brown that bit of their legs that is visible below the hemline as quickly as possible.

“This type of intense, rapid exposure is exactly what increases the risk of getting melanoma.”

Details of the study, which was funded by the US National Institutes of Health, is published in the journal Cancer Epidemiology Biomarkers and Prevention.

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